Yu D W, Pang S Y, Checkla D M, Freedberg I M, Sun T T, Bertolino A P
Department of Dermatology, Kaplan Cancer Center, New York University School of Medicine, New York.
J Invest Dermatol. 1991 Aug;97(2):354-63. doi: 10.1111/1523-1747.ep12480706.
Although it has been shown previously that an acidic (type I) "soft" keratin can interact with many basic (type II) "soft" keratins to form 10-nm intermediate filaments, it has been unclear whether "soft" keratins are compatible with the "hard" keratins typically found in hair and nail. To address this issue and to generate more structural information about hard keratins, we have isolated and sequenced a cDNA clone that encodes a mouse hair basic keratin (b4). Our sequence data revealed new information regarding the structural conservation of hard keratins as a group, being significantly different from soft keratins. Using expression vectors containing appropriate cDNA inserts, we studied the expression of this basic (b4) as well as an acidic (a1) mouse hair keratin in HeLa cells. The expression of these alien hair keratins in the transfected cells was surveyed using a panel of monoclonal and polyclonal antibodies. Our results indicated that the basic and acidic hair keratin readily incorporated into the existing endogenous soft keratin network of HeLa cells. Overproduction of hair keratin, however, occasionally led to the formation of cytoplasmic aggregates containing both hard and soft keratins. These data suggest that although small amounts of newly synthesized hair keratins can incorporate into the "scaffolding" of the preformed soft keratin filament network, possibly through dynamic subunit exchange, overproduction of hard keratins can lead to the partial collapse of the soft keratin network. These observations, along with the deduced amino acid sequence data, support and extend the concept that hard and soft keratins, although closely related, are divergent enough to justify their being divided into two separate subgroups.
尽管先前已表明酸性（I型）“软”角蛋白可与许多碱性（II型）“软”角蛋白相互作用形成10纳米的中间丝，但尚不清楚“软”角蛋白是否与毛发和指甲中常见的“硬”角蛋白兼容。为了解决这个问题并生成更多关于硬角蛋白的结构信息，我们分离并测序了一个编码小鼠毛发碱性角蛋白（b4）的cDNA克隆。我们的序列数据揭示了有关硬角蛋白作为一个群体的结构保守性的新信息，其与软角蛋白有显著差异。使用含有适当cDNA插入片段的表达载体，我们研究了这种碱性（b4）以及酸性（a1）小鼠毛发角蛋白在HeLa细胞中的表达。使用一组单克隆和多克隆抗体检测转染细胞中这些外来毛发角蛋白的表达。我们的结果表明，碱性和酸性毛发角蛋白很容易整合到HeLa细胞现有的内源性软角蛋白网络中。然而，毛发角蛋白的过量表达偶尔会导致形成同时含有硬角蛋白和软角蛋白的细胞质聚集体。这些数据表明，尽管少量新合成的毛发角蛋白可能通过动态亚基交换整合到预先形成的软角蛋白丝网络的“支架”中，但硬角蛋白的过量表达会导致软角蛋白网络部分坍塌。这些观察结果以及推导的氨基酸序列数据支持并扩展了这样的概念，即硬角蛋白和软角蛋白虽然密切相关，但差异足够大，足以证明它们应分为两个独立的亚组。
